The documents listed below are incorporated herein by reference:                1. Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs), IEEE 802.15.4e 2012;        2. Technical Profile Specification Field Area Network, Wi-SUN Alliance 2014; and        3. Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs), IEEE 802.15.4 2011.        
Channel hopping, while communicating between network devices (nodes), has been widely adopted in multiple wireless and wireline communication systems. Channel hopping essentially involves transmitting the radio signals on different carrier frequencies among many available sub-carriers at different instances of time. A pseudorandom sequence known to both the transmitter and receiver is usually used so that the transmitter transmits to the intended receiver on the channel where the receiver is listening. This improves robustness to external noise, and helps counter jamming and eavesdropping.
Channel hopping can achieve increased network throughput by permitting simultaneous data transfer over multiple channels between different pairs of nodes, and can enhance reliability in difficult channel conditions by exploiting channel diversity. Multiple technologies such as Bluetooth and Digital Enhanced Cordless Telecommunications (DECT) use channel hopping.
Channel hopping can be achieved through many different methods, for example, a synchronous method called Time Slotted Channel Hopping (TSCH), and an asynchronous method called Un-Slotted Channel Hopping (USCH), as defined document 1 referenced above. Many standards use a channel hopping MAC (Media Access Control) to define MAC protocols for different applications. For example, the Wi-SUN Alliance has proposed (see document 2 above) a Field Area Network (FAN) specification that uses USCH for smart grid applications.
In USCH, each node picks a hopping sequence and hops its receiver among the different channels. In each channel, a node spends a specified time called the dwell interval (also referred to herein as a channel hop interval or CHI). Many methods exist to track a receiver's USCH sequence, for example, the FH-Discover method proposed in document 2 above.
In USCH, channel hopping schedules are receiver-directed in that a transmitting node sends a transmission on the receiver's current channel hop (using a suitable collision avoidance technique such as Carrier Sense Multiple Access with Collision Avoidance, or CSMA-CA, to make a clear channel assessment, or CCA). If the transmission goes beyond the current CHI, then the transmission is continued into the adjacent (next successive) CHI, and the receiver continues listening on the current channel. If a transmission does so extend into the adjacent CHI, a second transmitter may try also to transmit to the receiver in that adjacent CHI, because the second transmitter assumes that the receiver is listening on the channel associated with the adjacent CHI. Thus, the transmission from the second transmitter will be lost, because the receiver has not switched to the channel associated with the adjacent CHI.
Some applications, like sensor networks, for example, have energy constraints. Hence, it becomes critical to provide for low-power operation to lower energy consumption. Many different low-power modes of operation have been proposed. Techniques like the inactive slot in super frame (defined in document 3 above), and a similar technique used in LLDN networks (see document 1 above) use dedicated pre-allocated sleep time for the whole network or part of the network, whereby all nodes in a target region can go to sleep. The needed coordination is achieved using synchronous beacons from coordinators.
When there is no global network level synchronization, and each node has its own sleep schedule, conventional methods like CSL (Coordinated Sample Listening) or RIT (receiver initiated transmissions) may be used. In CSL (see document 1 above), the transmitter uses wake up frames longer than the receiver's sleep interval to transmit to an unsynchronized receiver. The receiver sleep interval must either be a fixed value for all nodes, or limited to a maximum value for all nodes, so that a transmitter can know the minimum duration of the wake up frame.
In RIT (see document 1 above), the receiver wakes up periodically to request a transmission. A node intending to send a transmission to the receiver listens until it hears the receiver's request, and then sends the transmission to the receiver. CSL and RIT are typically used for single channel operation. Multiple channel extensions of these techniques would involve repeating the techniques for multiple different channels.